1. Field of the Invention
The present invention relates to an inkjet printer head, i.e., a recording head for use in an inkjet recording device.
2. Discussion Of Related Art
As one of recording devices that record an image on a recording medium such as a recording sheet, there has conventionally been known an inkjet printer that ejects droplets of ink toward a recording medium and thereby records an image on the medium. Recently there has been a tendency that the inkjet printer employs an increased number of ink ejection nozzles to perform recording (i.e., printing) at an increased speed. Accordingly the inkjet printer employs an increased number of pressure chambers (i.e., individual ink chambers) corresponding to the increased number of ink ejection nozzles, respectively. In the case where the inkjet printer is for recording a full-color image, the inkjet printer employs a plurality of groups of pressure chambers corresponding to a plurality of color inks (e.g., cyan, magenta, yellow, and black inks), respectively, and a plurality of manifolds (i.e., common ink chambers) each of which supplies a corresponding one of the color inks to a corresponding group of pressure chambers. In this case, each of the manifolds is provided in the vicinity of the corresponding group of pressure chambers.
FIG. 10 shows a recording head 101 for use in a conventional inkjet recording device. The recording head 101 includes a cavity unit 131 and a piezoelectric actuator 151. The cavity unit 131 has a plurality of nozzle holes 141a (i.e., ink ejection nozzles) that eject droplets of an ink; a plurality of pressure chambers 149a (i.e., individual ink chambers) that communicate with the nozzle holes 141a, respectively; and a manifold (i.e., a common ink chamber), that is, a pair of manifold holes 144a, 145a that temporarily stores the ink and supplies the ink to each of the pressure chambers 149a. The piezoelectric actuator 151 changes a pressure of the ink in each of the pressure chambers 149a and thereby ejects, from a corresponding one of the nozzle holes 141a, a droplet of the ink toward a recording sheet.
The cavity unit 131 includes a nozzle sheet 141, and a stacked structure consisting of a plurality of stacked sheets. Those stacked sheets include a spacer sheet 142; a damper sheet 143; two manifold sheets 144, 145; a ceiling sheet 146; an aperture sheet 147; a base sheet 148; and a cavity sheet 149, and are bonded with an adhesive to each other. Communication holes 146a, 148a and communication passages 147a through which the pair of manifold holes 144a, 145a communicates with the pressure chambers 149a, respectively, are formed in the sheets 146, 148, 147; and communication holes 142a, 143b, 144b, 145b, 146b, 147b, 148b through which the pressure chambers 149a communicate with the nozzle holes 141a, respectively, are formed in the sheets 142, 143, 144, 145, 146, 147, 148. The damper sheet 143 has a recess 143a functioning as a damper chamber that damps vibration of the ink present in the pair of manifold holes 144a, 145a. The recess 143a opens toward the nozzle sheet 141.
Generally, the communication holes 146a are through-holes that are formed through the thickness of the ceiling sheet 146, and have a circular cross-section shape whose diameter ranges from 150 μm to 250 μm. Therefore, as shown in FIG. 11, if a small air bubble, B1, whose diameter ranges from 0.3 mm to 1.0 mm, flows from an upstream-side portion of the pair of manifold holes 144a, 145a toward a downstream-side portion of the same, and remains just under each of the communication holes 146a, the small air bubble B1 blocks or closes the each communication hole 146. Thus, the ink cannot be supplied to a corresponding one of the pressure chambers 149a, or ejected from a corresponding one of the nozzle holes 141a. 
FIG. 12 shows such a large air bubble, B2, that blocks the pair of manifold holes 144a, 145a as a whole. In this case, as the ink is consumed through the nozzle holes 141a corresponding to the downstream communication holes 146a currently located on the downstream side of the large air bubble B2, the large air bubble B2 is moved downstream toward the downstream-side portion of the pair of manifold holes 144a, 145a. Since the large air bubble B2 is moved little by little, each communication hole 146a that has temporarily been closed by the air bubble B2 is again supplied with the ink, and accordingly the ink is again ejected from the corresponding nozzle hole 141a. However, when the large air bubble B2 reaches the downstream-side end of the pair of manifold holes 144a, 145a, the air bubble B2 becomes unable to move any more and stays there. Thus, the communication hole or holes 146a, provided around the downstream-side end of the pair of manifold holes 144a, 145a, remain closed by the large air bubble B2, and accordingly the ink cannot be ejected from the corresponding nozzle holes 141a. 
The nozzle holes 141a that have failed because of staying of the air bubble B1, B2 can be restored to their normal condition, by being subjected to a known purging operation. However, if one or more nozzle holes 141a fail because of staying of the air bubble B1, B2 during a recording operation of the inkjet recording device, those nozzle holes 141a cannot be instantaneously subjected to the purging operation and cannot be restored to their normal condition.
Meanwhile, Japanese Patent Application Publication No. 11-20186 or its corresponding U.S. Pat. No. 6,749,296 proposes an inkjet recording device that employs, for the purpose of supplying, in spite of staying of air bubbles, a sufficient amount of ink to a recording head, a first ink supply passage that is provided with a plurality of radial ridges that are spaced from each other by an angular pitch assuring that the radial ridges can capture the air bubbles.
However, the inkjet recording device disclosed by the above-indicated document is one that additionally employs a second ink supply passage through which the ink flows from an ink cartridge toward the first ink supply passage; and a filter that is provided in an area where the first and second ink flow passages are connected to each other. Therefore, the disclosed technique cannot be used as a countermeasure to deal with the air bubbles B1, B2 produced in the pair of manifold holes 144a, 145a of the cavity unit 131 of the recording head 101.